<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>
	<body>
		<script type="text/javascript">
			//用递归打印1-3
			function print1_3 (n) {
				document.write(n + "<br />")
				n++
				if (n<=3) {
					print1_3(n)
				}
				document.write(n + "<br />")
			}
			print1_3(1)
		</script>
	</body>
</html>
